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DTMF Telephone

Trainer ST2654

An ISO 9001 : 2000 company

Operating Manual

Ver 1.1

94-101, Electronic Complex Pardeshipura,

Indore- 452010, India

Tel : 91-731- 2570301/02, 4211100

Fax: 91- 731- 2555643 email : [email protected]

Website : www.scientech.bz

Toll free : 1800-103-5050

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ST2654

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ST2654

DTMF Telephone Trainer

ST2654

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Table of Contents

Introduction

Features

Technical Specifications

Safety Rules

Mimic Board Diagram

Block Diagram of DTMF Telephone Trainer

Theory of Operation

Experiments

Experiment 1

Study of the Telephone by Line Connection or

By Simulated Power Supply

Experiment 2

Study of the Polarity Protection Block

Experiment 3

Study of the Working of Voltage Dropper Circuit in Telephone

Experiment 4

Study of the Working of Ringer Circuit

Experiment 5

Study of the Working of Key Matrix Section

Experiment 6

Study of the Working of Dialer Section & of DTMF Signals

Using High Pass Filter and Low Pass Filter

Experiment 7

Study of the Working of Sound Section or Speech Section

Experiment 8

Study of the Telephone Trainer by Switched Faults

Glossary

Warranty

List of Accessories

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ST2654

Introduction

Scientech Telephone Trainer ST2654 is an ideal training equipment to teach the operation of Telephone. It is demonstrator cum Trainer specifically designed for the study of working of telephone.

This operation manual must be used contemporarily by the teacher & the student. It is concerned with the notions of theory and examples of exercises.

The theory represents a complete reference for the introduction to the treated subjects, so the teacher can use it as an exhaustive text to develop his educational program, or it will be reference from which to start a deeper development.

One of the features of this trainer is fault simulation to train on actual fault finding by simulating faults in the instruments. The fault created in the instrument in no way affects or damage the instrument.

The exercises, conceived to provide a practical approach to the subjects, enables a deep analysis of the same subjects and will guide the student, step by step to the complete understanding of each function included in the trainer and the way to carry it out.

The trainer has been so designed to meet the requirements of electrical & electronics engineering student of the degree level. The trainer has been so presented that any engineering student with a basic knowledge of the various electronic building blocks and fundamentals of communication system will have no difficulty in understanding the trainer.

We hope our attempt will help the user to understand the basic concept and working of telephone.

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ST2654

Features

Self contained easy to operate trainer.

On board telephone line connection facility.

Functional blocks indicated on board mimic.

Operation manual provided.

Compact size.

Various Test Points & LEDs are provided on board.

Switch faults are provided to study different effects on circuit.

Tone Dialing as well as Pulse Dialing facility.

High Pass & Low Pass Filters to study the DTMF frequencies.

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Technical Specifications

Operation

: 1. Stand Alone

Handset

Key Board

Dialer

Indications

Control

Speech Path

Dial Pulse Ratio

Input Power

Test Points

Switched Faults

Power

Dimensions (mm)

Weight

2. One DOT/EPABX Line connection Port

: Handset connection Port (RJ-45)

: 3

×

4 Matrix Key Board

: DTMF and Pulse dialing redial up to 32 digits,

‘On/Off’ Hook switch

: Line on / Pulse Dialing Indication,

Tone Dialing Indication

: Ringer Volume Control

: Non Blocking

: 67 : 33% Make Break Ratio (approximately)

: From Internal Power Supply

From Telephone Line

: 25 numbers Test Points are provided to observe various signal/ voltages to understand the working of Telephone.

: 4 Nos.

: 230V, +/- 10 %, 50Hz

: W 420 x H 100 x D 255

: 2.5 Kg. (approximately)

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Safety Rules

Keep this operating manual at hand for any further help.

After the packaging has been removed, set all accessories in order so that they are not lost and check the equipments integrity. In particular, check that the equipment is integral and shows no visible damage.

This equipment must be employed only for the use it has been conceived, i.e. as educational equipment, and must be used under the direct survey of expert personnel.

Any other use is not proper and so dangerous. The manufacturer can not be considered responsible for eventual damages due to not proper, wrong or unreasonable uses.

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Figure 1

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Block Diagram of DTMF Telephone Trainer

Figure 2

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Theory of Operation

The basic objective of DTMF Telephone Trainer is to study all the signals or voltages in different sections of the circuit. When receiver of telephone is in on hook condition then circuit gets + 40V to 60V (approximately) supply from telephone line. But because of blocking capacitor this supply does not reach to ringer section. In this condition when exchange gives ring signals then these 20 Hz AC Signals are passed through blocking capacitor and hence it goes to ringer section so that we can hear ring from buzzer. But when we pick up the receiver voltage dropper section comes in to the picture. Now +60V (approximately) drops up to +12V and this is used for other operations of telephone circuit. First Tip and Ring signals are passed through polarity protection bridge. So if DC supply connection wires coming from exchange reversely connected then also because of polarity protection bridge right polarity obtained for telephone circuitry. Key matrix have a special type of arrangement of switches. Here if we press any switch then corresponding row & column pins are shorted. This will provide a different function for different switches.

This trainer is able to work on both pulse and Dual Tone multi frequency (DTMF) modes. This mode selection is possible with * switch. For pulse mode dialer section generates the pulses according to the number of that particular switch. For example, if we press '4' then '4' pulses are generated and sent to exchange. According to these pulses exchange got the identity about the pressed switch number.

In the same way in tone mode for every switch a row and column frequencies are there. It is the group of high and low frequencies so when we press a particular switch corresponding High and Low frequency signals are sent to exchange. According to these signals exchange got the identity about the pressed switch number. Exchange have High Pass and Low Pass Filter circuits for identification.

Especially we have High Pass & Low Pass Filter in our trainer kit which enables us to observe the signals. It is not the part of telephones. It is of exchange. Sound signals are amplified by sound amplifier section also it amplifies the dial tone signals from dialing generator section.

Recommended testing instruments for experimentation

1.

Digital Multi-meter 3½ digit.

2.

CRO with Component Tester facility Model Scientech 201

3.

DSO Model Caddo 9100

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Experiment 1

Objective :

Study of the telephone by line connection or by simulated power supply

Procedure :

1.

Connect line input to the line connector i.e. Tip & ring wires from exchange.

2.

Now trainer is ready for the experimental studies of different sections. In case if line input is not available in laboratory, then connect supply output (provided on trainer) to TP1 and TP2 by banana patch cards.

3.

Now trainer is ready for the experiments by simulated supply (maximum experiments can be performed by this input) trainer gets internal +12V DC so it is used by different blocks of the trainer.

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Experiment 2

Objective :

Study of the polarity protection block

"Telephone set is connected with telephone exchange with 2 wires which are used for transmission and reception."

Exchange provides 40 Volt DC (approximately) to telephone set for its operation,

Since electronic devices are working at correct polarity DC voltage so wrong connections of these wires to telephone may damage the circuitry. To prevent it bridge rectifier is used. That is why it is also called as a polarity protector. It is not possible to find out the positive and negative terminals from line so there may be the possibility of wrong connections. But since diode are only working with forward biasing so bridge circuit always gives correct polarity supply to other circuitry of telephone for working. Hence interchanged connections does not affect the telephone circuit. To make the voltage constant a VDR (Voltage Dependent Resistor) is used

VDR is just like a resistor, whose resistance varies according to voltage variation. So the voltage providing for telephone circuit will be stabilized.

Procedure :

By Telephone exchange Line :

1.

Make fault switches in off condition.

2.

Connect line connector to telephone trainer board.

3.

Measure voltage at TP3 in ‘Off’ HOOK or ‘On’ HOOK condition and observe the polarity by DMM.

4.

Now interchange the line wires (from the line cable connector which is coming to laboratory).

5.

Again measure voltage at TP3 in ‘Off’ HOOK or ‘On’ HOOK condition and observe the polarity.

It should be same as previous. It means interchanging of Tip & ring wires does not affect the polarity. It is polarity protection.

By Simulated Supply Line :

6.

Disconnect the telephone exchange line connector and connect supply output to

TP1 & TP2

7.

Repeat step 3 to 5.

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Experiment 3

Objective :

Study of the working of voltage dropper circuit in telephone

Voltage dropper or switching circuit or current limiter is made up of number of transistors when hook switch is in ON-hook condition at that time exchange provides

60V (approximately) supply to telephone set. When the receiver is picked up from the cradle, it is the job of this section to drop the DC input supply available in the telephone line to the operating voltage range. Mainly three transistors are used for voltage dropper function, these are Q3, Q2 & Q1. There main function is to provide dropped regulated voltage to dialing generators & amplifier section.

Procedure :

1.

Make fault switches in off condition.

2.

Connect line connector to telephone trainer board. Measure the voltage at TP25

(output of voltage dropper section) in ON hook condition (i.e. hook switch is pressed. It is the normal condition of phone when receiver is kept on hook switch.) It is approximately 60V DC.

3.

Now release the hook switch means make off hook condition & measure the voltage at TP25. It is approximately to 10V. Now this low voltage is used as operating voltage for telephone set.

4.

If simulated supply line is used then input voltage is +12V so it drop up to 10V

(approximately).

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Experiment 4

Objective :

Study of the working of ringer circuit

Ringer circuit is mainly having a IC 1240. From telephone line one wire is directly connected to pin 8 of IC 1240 & another with a capacitor (105 K) C22 & resistor R25

(2K2) to Pin No. 1.

In ‘On’ Hook condition 40 DC (approximately) coming from line is not going upto ringer circuit because of the blocking capacitor C22 but when ring signals are coming that is of 20 Hz frequency then these AC signals are passed through the capacitor & reaches up to ringer IC's Pin 1.

Now these ring signals from pin 1 and 8 are rectified first & filtered by capacitor C23

(10µ) on pin7. Hence with this DC ring signals are generated by IC & obtained at pin5 of IC 1240. These amplified ring signals are given to speaker or buzzer with volume controlled potentiometer RV1 (100K) so that we can hear the ring signals.

Between pin 2 & 3 a capacitor C24 (104K) is connected for the discharging of the signal & between 2 & 4 a resistor R26 (22K) is connected for ringing speed control.

Procedure :

1.

Make all the fault switches in ‘Off’ condition.

2.

Connect the line connector to telephone trainer board.

3.

When trainer is in ‘On’ hook condition then there is no AC voltage on TP5 (due to blocking capacitor effect).

4.

Now call on this telephone from some other telephone.

5.

As ring signal are received by trainer board, observe them on TP5. It is 20 Hz

AC signal with high amplitude.

6.

TP4 will give you the ring signal which is directly coming from exchange.

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Experiment 5

Objective :

Study of the working of key matrix section

The key pad connected on trainer kit is of 3

×

4 matrix total 12 push buttons are there which are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, *, #.

These switches are connected in 4 Rows & 3 Columns in such a way that every switch is having relation with one row & one column. When switch is pressed that row is shorted with corresponding column. These row & column tracks are connected with row & column pins of dialer IC 91214B. When switch is pressed signal from column pin of dialer IC goes to row pin through push button. Hence dialer IC gets the information about row & column of that switch which is pressed.

R1

R2

R3

R4

C1

1

4

7

*

C2

2

5

8

0

C3

3

6

9

#

For example :

When 1 is pressed column pin 15 is shorted with row pin 12 of dialer IC. It means C1 is shorted with R1 & dialer IC gets the information that switch between pin 15 & 12 is pressed.

By pressing different Key switches different row and column pins of dialer IC are shorted.

These are as follows.

Push Button

0

1

2

3

4

5

6

7

8

9

*

#

Pins to be shorted of dialer IC

18-13

15-12

15-13

15-14

16-12

16-13

16-14

17-12

17-13

17-14

18-12

18-14

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Procedure :

1.

Make all the fault switches in ‘Off’ condition.

2.

To understand the working of key pad block there is no need to connect the line or supply input.

3.

Now use multimeter (low resistance range) or component tester facility of CRO.

4.

Press 1 of keypad since 1 is making the connection of R1 with C1 so measure resistance between TP17 & TP14. It will be low. If released it will be high. If component tester pattern is observed on CRO between TP17 & TP14.

Figure 3

5.

In the same way other switches of the key pad can be tested. Now how these are working electrically that we will see in dialer section.

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ST2654

Experiment 6

Objective :

Study of the Working of Dialer Section & of DTMF Signals Using High Pass

Filter and Low Pass Filter

The dialer circuit in this telephone trainer is made up of the IC UM91214 B and some other related components. This IC has the facility to select the tone or pulse dialing. In the pulse dialing mode, the number key pressed on the keypad to dial number are decoded by this IC and based on the pressed number this works as a pulse circuit. For the DTMF dialing the DTMF sound tones are provided by this IC to the sound amplifier IC TEA 1062A from where this signal is amplified and passed on to the telephone line.

A 3.58 MHz crystal is connected in between Pin 3 & 4 of the dialer IC. This crystal or ceramic resonator works as time base for the oscillator in the dialer IC. This helps the dialer IC to generate accurate DTMF signal.

The number dialed from the key matrix is converted into tone or pulse dialing signal by the IC UM91214 in the dialing generator section. In the pulse dialing mode, based on the key pressed this IC generates number of ‘On–Off’ pulses for example - If you press number 4 on the key pad this IC will send 4 ‘On–Off’ pulses to telephone exchange.

This ‘On-Off’ signals turns ‘On’ and ‘Off’ 10 times in each second and there is a delay of around 1 second between the ‘On-Off’ pulse of different numbers being dialed.

Pin 1 of this IC is

HK

i.e. Hook switch input. This inverter input pin detects the state of the Hook switch contact. Pin 2 is mode input pin. It will select the dialing mode from either tone or pulse. Pin 3 & 4 are oscillator pins. Crystal is connected between these Pins. Pin 5 is negative supply (ground here). Pin 6 is positive supply.

From pin 7 tone dialing output comes out, from pin 11 pulse dialing output comes out, pin 8 is used for mute function and pin 9 is mode indication by LED. Pin 12, 13, 14 are column pins and pin 15, 16, 17, 18 are row pins.

When any switch from key pad is pressed pin 11 gives pulse output or pin 7 gives tone output (depends on mode selection) at that time exchange get amplified dial tone cut signals through voltage dropper section, hook switch and bridge network.

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Upper Band Frequency

Procedure :

1.

Connect line connector to telephone trainer board.

2.

Press * switch of key pad in ‘Off’-Hook condition, tone LED lits.

3.

Trainer is set for tone mode.

4.

Now if any switch of key pad is pressed DTMF output is generated. It is the combination of high frequency signal and low frequency signal.

5.

At TP8 crystal oscillator's 3.5 MHz frequency output is obtained if any switch pressed.

6.

Now press hook switch. Trainer comes out of tone mode and now it is in pulse mode.

7.

Now if any switch of keypad is pressed corresponding number of ‘On–Off’ pulses are generated and obtained at TP11.

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DTMF Output from Dialer

Figure 4

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Figure 5

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Figure 6

II by Simulated Supply :

8.

Disconnect the actual line connector from mimic board.

9.

Connect simulated supply line.

10. Repeat steps 2, 3, 4, 5 of this experiment.

11. Now observe TP12 and TP13 these will gives you the corresponding high and low frequency signal of switch pressed.

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Pulse Diagram during dialing a number High Pass Filter Output

Figure 7

Low Pass Filter output

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Figure 8

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Note : Since chebyshev low pass filter have ripple, so to get the clean waveform on oscilloscope use it in normal mode and adjust with level potentiometer.

This filter circuitary is made up of 2 active filters, a high pass one and a low pass one, each carried out with 4 operational amplifiers. The chebyshev topology of the 8th order has been used with 1 dB of ripple. The circuit receives 2 tones of DTMF signal across its input and separates them and sending them to the outputs of "High group"

(1209, 1336, 1447 Hz) and "Low group".

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ST2654

Experiment 7

Objective :

Study of the Working of Sound Section or Speech Section

The reception and transmission of sound signal is controlled by the IC - TEA 1062A in the telephone trainer A microphone is used as transmitter and a speaker is used as receiver. The main functions of this circuit are

1.

The input received from the microphone is amplified and provided to exchange through the telephone line.

2.

The signal coming in the telephone line is amplified and provided to the speaker.

3.

Dial tone signals coming in from the dialing generator section of the exchange is amplified and provided to the speaker.

The pin No. 13 of this IC is microphone input. This signal is sent to the exchange through the telephone line and voltage dropper section. Then from exchange this signal reaches up to the telephone instrument of the number dialed by us. When some one calls on this telephone the signal reaches up to pin 13 of the sound amplifier IC through polarity corrector and the voltage dropper section. This signal is amplified by the IC and provided as output at Pin No.4. Then from pin 4 the signals are sent to speaker so that we can hear the sound.

Procedure :

1.

Connect line connector of actual telephone line to mimic board.

2.

Make all the fault switches in off condition.

3.

You can hear the dial Tone as you make the telephone in ‘Off’ hook condition.

4.

Now make a call by dialing numbers. This dial tone can be heard in speaker of handset according to number pressed.

5.

Now during voice communication you can observe on TP23 receiving input sound signals as well as signals coming from another telephone on same point.

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Experiment 8

Objective :

Study of the Telephone Trainer by Switched Faults

Fault 1

Symptoms

Section

Problem

Fault 2

Symptoms

Section

Problem

Fault 3

Symptoms

Section

Problem

: No operation in pulse mode

: Dialer section

: Pin No.6 of dialer IC is +ve supply so if we switch ‘On’ fault 1 this supply not reaches up to pin 6 of IC 91214B. So pulse mode is not working.

: No ring signals

: Ringer section.

: Pin 8 one 1240 is ring signal input coming from line. If we press fault 2 then this ring signal does not reaches up to pin 8 of IC

1240 so we can not hear the ring signals.

Fault 4

Symptoms

Section

Problem

: No working in Tone mode

: Sound Section

: From pin 7 of dialer IC DTMF signal are coming out, which are going to sound IC 1062A for amplification. If we press fault 3 then tone output is OK at dialer section but not reaches for amplification so not reaches up to exchange and hence tone mode is not working.

: 1. No dial Tone hearing

2. No sound Signal

: Sound section

: Sound output from Pin 4 then of IC 1062A is going to speaker so if we press fault 4 then this output signals are not going up to speaker and hence you can't hear the sound.

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Glossary

Abbreviated Dialing (AD) :

Preprogramming of a caller's phone system or long distance Company’s exchange to recognize a 2- to 4- digit number as an abbreviation for a frequently dialed phone number and automatically dial the whole number.

Access Line (AL) :

A telephone circuit which connects a customer location to a network switching center.

All Trunks Busy (ATB) :

A signal tone indicate all lines or trunks in a routing group are busy.

Alternate Route (AR) :

A secondary communication path used to reach a destination if the primary path is unavailable.

Alternate Use (AU) :

The ability to switch communication facilities from one type to another i.e. voice to data etc.

Area Code (AC) :

A number associated to different areas, used for direct distance dialing (DDD/STD) on the telephone system. A similar global numbering plan has been established for international subscriber dialing (ISD)

Audible Ringing Tone (ART) :

An audible signal heard by the calling party during the ringing-interval

Authorization Code (AC) :

A 5- to 14 digit number entered using a touch-tone phone to identify the caller as a customer of the long distance service. Used primarily to verify the caller as a customer and to bill the calls.

Automatic Call Distributor (ACD) :

A switching system designed to queue and / or distribute a large volume of incoming calls to a group of attendants to the next available "answering" position.

Automatic Dialing Unit (ADU) :

A device which is programmed with frequently called numbers. The caller pressed one to three digits code and the preprogrammed number is automatically dialed into the phone circuit.

Automatic Identification of outward Dialing (AIOD) :

The ability of some exchanges to provide an itemized breakdown of charges

(including individual charges for toll calls) for calls made by each telephone extension.

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Automatic Number Identification (ANI) :

On long distance calls, the process by which the local company passes a caller's local billing phone number to his/her long distance company when an STD or ISD call is made with ANI a caller's long distance carrier knows whom (what phone number) to bill without requiring the caller to enter any extra digits to be identified.

Baud :

A unit of signaling speed. The speed in Baud is the number of discrete conditions or signal elements per second.

Break :

A means of interrupting transmission, a momentary interruption of a circuit.

Busy Hour (BH) :

The time of day when phone lines are most in demand.

Busy Tone (BT) :

A tone that is interrupted at 60 ipm (impulses per minute) to indicate that the terminal point of a call is already in use.

Carrier System (CS) :

A system for providing several communication channels over a single path.

Central Office (CO) :

A building containing the local telecom exchange which provides local telephone service. Also the physical point from where calls enter the distance network. Also referred to as Class 5 office, end office, or local exchange office.

Codec :

Coder-Decoder. Used to convert analog signal for transmission over a digital media and back again to the original analog form.

Cross Talk (CT) :

The unwanted energy (speech or tone) transferred from one circuit to another circuit.

Decibel (DB) :

A unit measurement represented as a ratio of two voltages, current or powers and is used to measure transmission loss or gain.

Dedicated Access Line (DAL) :

An analog special access line going from a caller's own equipment directly to a long distance company's exchange. Usually provided by a local telephone company.

Delay Dial :

A dialing configuration whereby local dial equipment will wait until it receives the entire telephone number before seizing a circuit to transmit the call.

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Dial Pulsing (DP) :

The transmitting of telephone address signals by momentarily opening a DC circuit a number of times corresponding to the decimal digit which is dialed.

Dial Selective Signaling (DSS) :

A multipoint network in which the called party is selected by a prearranged dialing code.

Dial Tone (DT) :

A tone indicating that automatic switching equipment is ready to receive dial signals.

Direct Distance Dialing (DDD) :

A basic toll service that permits customers to dial their own long distance call without the aid of an operator. Also known as STD, Subscriber's Trunk Dialing.

Direct Inward Dialing (DID) :

A PBX or CENTREX feature that allows a customer outside the system to directly dial a station within the system.

Dual Tone Multi-frequency (DTMF) :

Also known as Touch-Tone. A type of signaling which emits two distinct frequencies for each dialed digit.

Duplex Signaling (DS) :

A long-range bidirectional signaling method using paths derived from transmission cable pair. It is based on a balanced and symmetrical circuit that is identical at both ends.

Echo :

A signal that has been reflected or otherwise returned with sufficient magnitude and delay to be perceived by the speaker.

Echo Suppressor :

A device which detects speech signal transmitted in either direction on a four-wire circuit, and introduces loss in the direction of transmission.

Electronic Key Telephone Sets (EKTS) :

A generic term indicating key telephones with built in microprocessors which allow access to PBX-like features as well as access to multiple lines, using 2 to 4 pair wiring.

Electronic Switch :

Modern programmable exchange (often denoted ESS, for Electronic switching system) used in most new exchanges. Completely to solid state electronics, as opposed to older electro-mechanical exchanges.

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Electronic Switching System (ESS) :

Used as a station instrument on a PBX. Also a bell system term for electronic exchange switching equipment.

Equalization :

The procedure of compensation for fluctuation in circuit amplitude delay or distortion.

Erlang :

A unit of traffic intensity. One Erlang is the intensity at which one traffic path would be continuously occupied. e.g. one call per hour.

Exchange :

A telephone switching center

Facsimile (FAX) :

The transmission of pictures maps or other documents via communications circuit using a device which scans the original document, transforms the image into coded signal and reproduces the original document at a distant point.

Full Duplex (FD) :

A circuit which allows transmission of a message in both direction at the same time.

Half Duplex (DO) :

A circuit for transmitting or receiving signals in one direction at a time.

Hook-Switch :

The device on which the telephone receiver hangs or on which a telephone handset hangs or rests when not in use.

The weight of the receiver or handset operates a switch which opens the telephone circuit, leaving only the bell connected to the line.

Keyset :

A telephone instrument having an appearance of two or more telephone lines which can be accessed by a button on the face of the set.

Leased Lines (LL) :

Any circuit or combination of circuit designated to be at the exclusive disposal of a given subscriber.

Modem :

A device which modulates and demodulates the signals on a carrier frequency and allows the interface of digital terminals with analog carrier system.

Numbering Plan Area (NPA) :

A geographical division within which no two telephones will have the same number

"N" is any number between "2" and "9" : "p" is always "1" or '0' and "A" is any number excluding "O". Commonly referred to as "area code”.

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Off-Hook :

The condition which results when a telephone is lifted from its mounting allowing the hook-switch to operate.

Off Premises Extension (OPX) :

An extension telephone or keyset that is geographically separated from its Associated

PBX.

On-Hook :

The condition which results when a telephone is placed on its mounting which causes the hook-switch to open its contacts.

Private Branch Exchange (PBX) :

A private phone system (exchange) used by medium and large companies which is connected to the public telephone network and perform a variety of in house routing and switching.

User usually dial "9" to get outside systems to the local lines.

Repeater :

An electronic device used to amplify signals which have become too weak.

Service and Equipment record (SAER) :

A list of equipment billed to customer by typing. Quantity, monthly charge, location and billing dates.

Signal To Noise Ratio (SNR) :

Ratio of the signal power to the noise power in a specified bandwidth, usually expressed in dB

Switched Access (SA) :

Connection between caller's phone system and exchange of chosen long distance carrier when a regular local lines is made. Also the connection between the exchange of caller's long distance carrier in the distant city and the phone being called.

Tandem :

A switching arrangement in which the trunk from' the calling office is connected to a trunk to the called office through an intermediate point.

Telegraph (TELEX) :

A system employing the interruption or change in the polarity of DC current signaling to convey information.

Telephone :

A device which converts acoustical (sound) energy into electrical energy for transmission to a distant point and received from another point.

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Transmission Speed (TS) (WPM) (BAUD) (BPS) :

Number of pulses or bits transmitted in a given period of time usually expressed as

Bits Per Second (BPS) or words Per Minute (WPM)

Trunk :

A telephone circuit or path between two exchanges at least one of which is usually a telephone company central office or switching center

Wide Area Telecommunications Service (WATS) :

WATD permits customer to make (OUTWATA) or receive (INWATS) long distance calls and to have them billed on a bull rather than individual call basis. The service is provide within selected service area or bands by means of special private access lines connected to the public telephone network via WATS- equipped central offices. A signal access line permits inward or outward service, but not both.

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ST2654

Warranty

1.

We guarantee the product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.

2.

The guarantee will become void, if

a)

The product is not operated as per the instruction given in the operating manual.

b)

The agreed payment terms and other conditions of sale are not followed.

c)

The customer resells the instrument to another party.

d)

Any attempt is made to service and modify the instrument.

3.

The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.

4.

The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.

List of Accessories

1.

Banana Cable ........................................................................................... 1 No.

2.

Telephone Handset ................................................................................... 1 No.

3.

Mains Cord............................................................................................... 1 No.

4.

Patch cords 16” ........................................................................................ 2 Nos.

5.

e-Manual .................................................................................................. 1 No.

Updated 15-05-2009

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